Generally, there are two kinds of reduction mechanisms for performing the speed reducing function during the loading or unloading of tapes in a tape recorder: the reduction mechanism using a worm gear of a large reduction ratio, and the reduction mechanism using a plurality of reduction gears.
However, the reduction mechanism using a worm gear has the disadvantage of occupying a large installation area, and difficulties are encountered in assembling it. Therefore, the reduction mechanism using a plurality of reduction gears is generally used, and this will be described below.
As shown in FIG. 1, a reduction mechanism 100 which performs the reducing function by means of a plurality of reduction gears is constituted such that: a reduction mechanism section 10 for reducing the revolution speed of a motor (not shown in the drawings) is installed on a main chassis 101; and a reduction mechanism section cover 20 covering the reduction mechanism section 10 is coupled with the main chassis 101 by means of screw members 21.
The reduction mechanism section 10 includes: a first revolution shaft 11 with a driving gear 17 and a pulley 18 attached thereon; a second revolution shaft 12 with a driven gear 19 installed thereon; and first and second fixed shafts 13,14 with a plurality of reduction gears 22-24, 25-27 freely rotatably installed thereon.
The conventional reduction mechanism 100 is installed in such a manner that first and second revolution shafts installing bushes 15,16 and first and second reduction gears installing fixed shafts 13,14 are press-fitted to proper positions on the main chassis 101.
Thereafter, the first and second revolution shafts 11,12 are fitted into the respective bushes 15,16, and a plurality of the reduction gears 22-24, 25-27 are fitted to the first and second fixed shafts 13,14 in such a manner that they should be meshed with each other so as for the revolutions of the motor to be reduced.
The main chassis 101 is turned upside down, and the pulley 18 for receiving the power from the motor is coupled with the end of the first revolution shaft 11.
After the completion of the installation of the reduction mechanism section 10 as described above, the main chassis 101 is turned upside down again. Then, the reduction mechanism section cover 20 is attached over the reduction mechanism section 10 and on the main chassis 101 by means of screw members 21, thereby completing the assembling of the reduction mechanism 100.
In the above described reduction mechanism for tape recorders, the first and second fixed shafts and the first and second bushes for installing the first and second revolution shafts are directly secured on the main chassis, and the first and second revolution shafts and the respective gears are installed, with the reduction mechanism section cover being installed thereafter. Due to such a complicated procedure, the distances between the shafts are varied caused by the machining inaccuracies and deformations of the main chassis, with the result that accurate operations become impossible. Further, due to the complicated assembling procedure, the productivity is lowered, and the manufacturing cost is increased.
Further, the reduction mechanism section is covered with a separate cover, so that the coupled portions can be displaced due to the vibrations of the motor, with the result that deviations in the meshes of the reduction gears occur. This brings the result that motor revolution losses occur, and that the loading and unloading of the tape are adversely affected, thereby deteriorating the reliability of the products.